Some engines operate according to a four stroke cycle comprising an intake stroke, a compression stroke, a power stroke, and an exhaust stroke. Other engines operate according to a two stroke cycle where the intake stroke is partially shared with the compression stroke and the exhaust stroke is partially shared with the power stroke. Some engines have been developed that can be selectively operated in a two stroke cycle during some conditions and a four stroke cycle during other conditions. In this way, the engine may exhibit higher power output through selective use of the two stroke cycle while achieving increased fuel efficiency through selective use of the four stroke cycle.
The inventor herein has recognized that some valves of the engine may undergo greater wear than other valves as the result of their more frequent use, particularly when transitions are performed between four stroke operation and two stroke operation. As such, asymmetric valve system wear may occur as a result of these transitions. To reduce asymmetric valve system wear, the inventor has provided a method that includes: operating the combustion chamber in a four stroke cycle by repeatedly opening a first exhaust valve of the combustion chamber once every four piston strokes via a first cam actuator while holding closed a second exhaust valve of the combustion chamber; after operating the combustion chamber in the four stroke cycle, operating the combustion chamber in a two stroke cycle by repeatedly opening the first exhaust valve once every four piston strokes via the first cam actuator and repeatedly opening the second exhaust valve once every four piston strokes via a second cam actuator during a different exhaust stroke than the first exhaust valve; and after operating the combustion chamber in the two stroke cycle, operating the combustion chamber in the four stroke cycle by repeatedly opening the second exhaust valve of the combustion chamber once every four piston strokes via the second cam actuator while holding closed the first exhaust valve of the combustion chamber. Note that this approach may be similarly applied to the intake valves in some examples.
In this way, the valves that were previously operated during the four stroke cycle may be periodically switched with the valves that were previously deactivated during the four stroke cycle, thereby enabling the valves to be operated on a more even basis while reducing asymmetric valve system wear. As such, the operating life cycle of the valve system may be increased.